A standard drill has a drill housing, a spindle projecting from the housing along an axis and rotatable about the axis, a chuck body rotatably fixed on the spindle, respective jaws on the chuck body, and a tightening body rotatable on the chuck body about the axis in a forward direction and in a reverse direction. Formations interconnecting the chuck body, jaws, and tightening body can move the jaws radially together on rotation of the tightening body in the forward direction on the chuck body and radially apart on rotation of the tightening body in the reverse direction on the chuck body. A setting element rotationally fixed on the drill housing displaceable axially on the chuck body between axially offset end positions and further formations between the setting element and the tightening body rotationally couple the setting element with the tightening body only in one of the end positions of the setting element.
Thus with this system the setting element is moved into its one end position, normally an axially forward position, and the drill's motor is actuated in the appropriate direction to tighten or loosen the chuck, as the setting element locks the tightening ring to the drill housing. Thus the user need exert no torque himself or herself to tighten or loosen the drill.
According to European 0,195 503 the setting element is an axially displaceable sleeve surrounding the chuck body that is pushed forward against a spring and held in place while the drill is operated for the tightening or loosening torque. When pushed forward teeth on the sleeve engage teeth on the tightening body to rotationally lock the two parts together. These teeth have angled flanks so they cam each other axially apart when the relative torque exceeds a predetermined limit, which normally leads to some chattering of the setting body on the chuck, along with concomitant wear. In addition to being subject to considerable wear, such a chuck has the substantial disadvantage that it can loosen in use, that is the tightening body can reverse rotate on the chuck body during drilling.
In my earlier U.S. Pat. No. 4,272,087 of 9 June 1981 a latching pin is displaceable chordally or secantally in a blind bore of the chuck body and is urged radially outward between teeth of an array of radially inwardly directed teeth on the tightening sleeve. An unlocking element can be rotated on the chuck to retract this pin which otherwise inhibits rotation of the sleeve on the chuck body. Thus this system effectively prevents the chuck from loosening by itself, but requires an extra step to be performed by the user before and after each tightening and loosening operation. If the unlocking element is not reset the chuck can loosen.